1. Field of the Disclosure
The present disclosure relates to an electrophoretic display device, and more particularly, to an eletrophoretic display device using a photo sensor in which a touch can be recognized any time by using photo sensors having a different channel width/length even if the peripheral illumination environment is changed.
2. Description of the Related Art
In general, an electrophoretic display device is an image display device using a phenomenon that colloidal particles move to either one of the polarities when one pair of electrodes to which a voltage is applied are immersed into a colloidal solution. The electrophoretic display device is a device in which a backlight is not used, having characteristics such as wide viewing angle, high reflectivity, high readability, low power consumption, and the like, thereby being anticipated as electronic paper.
The electrophoretic display device has a structure in which an electrophoretic film is interposed between two electrodes, and at least one of the two electrodes should be transparent to display images in a reflective mode.
When a pixel electrode is formed on a lower substrate of the two substrates and a potential is applied to the pixel electrode, charged particles within the electrophoretic film move to the pixel electrode or an opposite electrode thereof, thereby allowing images to be observed through a viewing sheet.
In addition to an electrophoretic display device using this principle, there is an in-cell touch-type electrophoretic display device in which photo sensors using the photo current of an amorphous silicon TFT are arranged on an element array, thereby sensing the photo current formed by light entering through an electronic ink film.
A touch-type electrophoretic display device using the foregoing photo sensor according to the related art will be described with reference to FIGS. 1 and 2.
FIG. 1 is a cross-sectional view schematically illustrating a touch-type electrophoretic display device using a photo sensor according to the related art. (Note: reference sign “50” in FIG. 1 is not recorded in the Description. It is suggested to delete “50” in FIG. 1).
FIG. 2 is a circuit diagram illustrating a touch-type electrophoretic display device using a photo sensor according to the related art.
Referring to FIG. 1, a touch-type electrophoretic display device using a photo sensor according to the related art includes a display substrate 11 formed with a switching element (Ts), a pixel electrode 29, a storage capacitor (not shown), a photo sensor element (S), and an output element (Tout), and an electrophoretic film 41 interposed therebetween on the display substrate 11.
The electrophoretic display device having the foregoing construction represents colors by moving black particles 45 or white particles 47 within the electrophoretic film 41 based on the polarity of the potential applied to the pixel electrode 29.
At this time, charged particles in the electrophoretic film 41 moves upward or downward by a potential difference between the pixel electrode 29 and a common electrode (not shown) by applying positive (+) or negative (−) direct current (DC) potential to the common electrode (not shown).
On the other hand, gate lines (not shown) for transferring scan signals and data lines (not shown) for transferring image data signals to actively drive a plurality of elements, for example, a photo sensor element (S), a switching element (Ts), and an output element (Tout), are provided on the lower substrate 11.
The gate and data lines intersect each other to define a unit pixel, and each unit pixel includes a photo sensor element (S), a switching element (Ts), an output element (Tout), and a storage capacitor (Cst), thereby functioning to control the polarity of the potential applied to each electrode and storing potential energy in the electrode.
Furthermore, the switching element (Ts) and output element (Tout) further include a pixel electrode 29 for applying an electric field to the electrophoretic film 41, and a protective film 25 formed with a low dielectric substance is interposed between the switching element (Ts) and output element (Tout), and the pixel electrode 29.
Furthermore, the photo sensor element (S) and switching element (Ts), and the output element (Tout), provided on the each unit pixel, include a gate electrode 13 branched from the gate line (not shown), a gate insulation film 15 formed on the gate electrode 13, an active layer 17 and an ohmic contact layer (not shown) laminated on the gate electrode 13, a source and a drain electrodes 21, 23 branched from the data line (not shown) and formed on the active layer 17. Here, the drain electrodes 23 of the switching element (Ts) and output element (Tout) are connected to the pixel electrode 29.
On the other hand, the electrophoretic film 41 is made of a base film 49, microcapsules 43, and an adhesive film 33, and laminated on the display substrate 11.
When an electric field is applied to the electrophoretic film 41 having the foregoing construction, pigment particles having a different color move in an opposite direction to each other, thereby dividing the inside of a microcapsule 43 into two regions having a different color.
A touch-type electrophoretic display device using a photo sensor having the foregoing construction according to the related art, referring to FIG. 2, the gate and source of a photo sensor element (S) are connected to an off-potential line and a potential line, respectively.
Furthermore, the drain electrode, which is an output terminal, is connected to a signal capacitor (C) and an input terminal (source) of the output element (Tout).
Furthermore, the photo current formed by light entering to a channel portion of the photo sensor element (S) flows in a direction of the signal capacitor (C) and output element (Tout) by a voltage applied to the potential line, and the signal capacitor (C) stores it as a signal potential.
On the other hand, another polarity of the signal capacitor (C) is connected to an off-potential line, and the off-potential line functions to form a predetermined amount of photo current by maintaining an off-potential in the photo sensor element (S).
Furthermore, the output element (Tout) is also a three-terminal element, and the control terminal (G) and output terminal (drain) thereof are connected to an output scan line and a signal output line, respectively.
Furthermore, when an on-potential is applied to an output scan line of the output element (Tout), it functions to output a signal potential stored in the signal capacitor (C) to the signal output line to read touch information.
However, a touch-type electrophoretic display device using a photo sensor according to the related art has a problem as follows.
When the photo sensor is formed by using an amorphous silicon element, or the like, a level of photo current generated at the relevant voltage is determined based on the width and length of a determined channel.
If the channel width becomes wider, photo current will be increased so that the photo current values will be saturated at a high illumination level, thereby limiting the performance of touch recognition.
On the other hand, if the channel width becomes narrower, photo current will be reduced so that the photo sensing output will be weakened, thereby similarly limiting the performance of touch recognition.
Due to the above-mentioned reasons, in case of a reflective-type electrophoretic display device according to the related art, insufficient photo current will be generated if ambient light is too dark whereas too much photo current will be generated to saturate the sensing output if it is too bright, thereby causing a touch recognition problem.
As a result, according to a touch method using the photo sensor according to the related art, a photo sensor element having a determined channel width and length is used, and thus it all the time creates an illumination region where a touch cannot be recognized based on its external illumination environment, thereby becoming a restraining factor in the manufacturing aspect.